Multivibrator



April 22, 1952 J, w, TAYLOR, JR 2,594,092

MULTIVIBRATOR Filed March 50, 1950 Negative Trigger Voltage 0 I 1 FTrigger 0 Tube IO Q) 3 E O Tube 12 o l L Tube 1| WITNESSES: INVENTOR X4201mm Time John W. Taylor, Jr.

iatented Apr. 22, 1952 MULTIVIBRATOR John W. Taylor, .lr., Baltimore,Md., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application March 30, 1950, SerialNo. 152,897

13 Claims.

This invention relates to multivibrators, and it has as objects tosimplify, and to reduce the number of components used in,multivibrators.

In some radar systems the antennas use a plurality of beams fordetermining the direction in which the antennas should be turned inorder to point towards the target. The radar set is operatedsequentially over these beams, and the signals are compared. Rapidcomparison is necessary for avoiding as much fluctuation in strength ofthe signals reflected from the target, as possible between lobing, sothat electronic switching is required. Two beams are sulficient to tracka target in azimuth, a scale-of-two multivibrator being used forcommunication; but three beams are required to track a target inelevation as well as azimuth, necessitating a scale-of-threemultivibrator.

Prior systems have used either a chain of three pairs of scale-of-twomultivibrators, or three interconnected pentodes. Either system requiresthree envelopes, one requiring three twin-triodes, and the otherrequiring three pentodes.

The pentode circuit operates by virtue of the fact that conduction canbe cut-off by either the control grid or the suppressor grid, one of twotubes in the triangle controlling the control grid of, and the other ofthe two tubes controlling the suppressor grid of, the third tube.

This invention provides a scale-of-three multivibrator in which twotubes in the triangle control the same grid of the third tube instead ofseparate grids. This enables one and one-half twin-triodes to be usedinstead of three pentodes, thus cutting the number of tubes required inhalf.

This invention is applicable not only to the rapid commutation of radarlobing antennas, but to repetition rate reducers for Geiger counters,and other applications requiring rapid electronic switching.

Anotherobject oi the invention is to simplify scale-of-threemultivibrators.

Another object of the invention is to reduce the number of electrontubes required for a scaleof-three multivibrator.

The invention will now be described with reference to the drawing, ofwhich:

Fig. l is a circuit schematic of a scale-of-three multivibratorembodying this invention; and

Fig. 2 is a graph illustrating the trigger poten tial pulses and thewaveforms of the potentials at the plates of the three tubes of Fig. 1.

The three triodes l0, II and I 2 have their cathodes interconnected andconnected through the cathode resistor l3 to ground.

The grid of the tube I0 is connected through the resistor 14 shunted bythe capacitor I5, to the plate of the tube l2, and through the resistorIt shunted by the capacitor H, to the plate of the tube ll. Likewise thegrid of the tube II is connected through the resistor I8 shunted by thecapacitor Hi, to the plate of the tube I0, and through the resistor 20shunted by the capacitor 2|, to the plate of the tube [2. Likewise thegrid of the tube I2 is connected through the resistor 22 shunted by thecapacitor 23, to the plate of the tube It, and through the resistor 24shunted by the capacitor 25, to the plate of the tube H.

The grid of the tube It is connected through the resistor 26 shunted bythe capacitor 21, to ground. Likewise the grid of the tube II isconnected through the resistor 28 shunted by the capacitor 29, toground. Likewise the grid of the tube I2 is connected through theresistor 30 shunted by the capacitor 33, to ground.

The plates of the tubes are connected through the load resistors 31 tothe positive terminal of the plate voltage source 32.

The resistors and capacitors connecting the grids and the plates of thetubes, and connecting the grids of the tubes to ground, are voltagedividers, and have such values that the conduction of either of thetubes will drop the grids of the others below cut-01f. However, the resistor and capacitor connecting a grid of one of the tubes to a plate ofone of the other two tubes, each have a different value than theresistor and capacitor connecting that grid to the plate of the other ofthe two tubes, so that the amount that grid remains below cut-ofidepends upon which of the said other tubes is conducting. By way ofexample, the tubes I0, I I and I2 may each be one-half of a 2651 with aplate voltage of 250 volts. The grid resistors 26, 28 and 30 may eachhave a resistance of 3.3 megohms. The resistors l4, l8 and 24 may eachhave a resistance of 6.8 megohms. The resistors i6, 20 and 22 may eachhave a resistance of 10.0 megohms. The resistors I3 and 3| may each havea resistance of 100,000 ohms. The capacitors 21, 29 and 33 may each havea value of 82 micro-microiarads. The capacitors I5, l9 and 25 may eachhave a value of 39 micro-microfarads. The capacitors I 1, 2| and 23 mayeach have a value of 27 micro-microfarads. I In operation, assuming thatall three multivibrator tubes conduct equally, a momentary increase inconduction of one of the tubes, say the tube ID, will increase thecathode voltages of the tubes l l and I2 due to the increased voltagedrop through the common cathode resistor is. At the same time, the gridvoltages of the tubes H and I2 will be reduced due to their voltagedivider coupling from the plate of the tube It]. These two effects tendto reduce the conduction of the tubes II and I2, and coupling from theirplates to the grid of the tube It tends to amplify the original increasein conduction of the tube It.

This process will continue until stability is reached with the tube ll]fully conducting, and the tubes H and I2 non-conducting. At this time,the grid voltage of the tube It will be 0. Its plate is connected to thegrid of the tube H through the resistor it having a value of 10.0megohms and the capacitor 17 having a value of 27 micro-microfarads, andis connected to the grid of the tube [2 through the resistor l4 having avalue of 6.8 megohms and the capacitor it having avalue of 39micro-microfarads. This difference in the values of the voltage dividerswill cause the tube 12 to have a grid voltage of -25 Volts and the tubeH to have a grid voltage of 37 volts.

Then when a negative trigger voltage is applied to the interconnectedcathodes of the tubes, the tube [2, the bias voltage of which is -25volts, will start conducting before the tube H, the bias voltage ofwhich is 37 volts, and then becomes fully conductive while the tubes IE)and It become non-conducting.

The grid bias voltage of the tube i2 will then be zero; the bias voltageof the tube H will. be -25 volts, and the bias voltage of the tube Itwill by -37 volts, so that when the next negative trigger voltage isapplied to the cathodes of the tube, the tube II will start conductingbefore the tube It, and then becomes fully conductive while the tubes [0and I2 become non-conduct- The grid bias of the tube Ii will then bezero; the bias voltage of the tube 13 will be 25 volts, and the biasvoltage of the tube ll will be 37 volts, so that on the next trigger thetube It will become conductive and take control again. Thus the triggerswill shift conduction cyclicly around the loop, each tube becomingconductive following every third trigger.

Fig. 2 of the drawing illustrates. the waveforms of the potentials ofthe plate circuits of the tubes as they are triggered in succession.

The circuit constants given in the foregoing,

were chosen for maximum stability, and as a result it was possible tovary the supply voltage three electron tubes each having a cathode, a

control grid and an anode, resistors connecting the grid of each tubewith the anodes of the other tubes, an anode voltage supply sourcehaving a positive terminal connected to said anodes, meansinterconnecting said cathodes, and a cathode resistor connecting saidinterconnected cathodes to the negative terminal of said source.

2. A scale-of-three multivibrator as claimed in claim 1 in whichcapacitors are shunted across said first mentioned resistors.

3. A scale-of-three multivibrator as claimed in claim 1 in whichresistors are connected between said grids and said negative terminal ofsaid source.

4. A scale-of-three multivibrator as claimed in claim 1 in whichcapacitors are shunted across said first mentioned resistors and inwhich resistors shunted by capacitors are connected between said gridsand said negative terminal of said source.

5. A scale-of-three multivibrator comprising first, second and thirdelectron tubes each having a control grid, a cathode and an anode, afirst resistor connecting the grid of said first tube with the anode ofsaid second tube, a second resistor having a higher value then saidfirst resistor connecting said control grid of said first tube with theanode of said third tube, a third resistor having the same value as saidsecond resistor connecting the grid of said second tube with the anodeof said first tube, a fourth resistor having the same value as saidfirst resistor connecting the grid of said second tube with the anode ofsaid third tube, a fifth resistor having the same value as said secondresistor connecting the grid of said third tube with the anode of saidsecond tube, a sixth resistor having the same value as said firstresistor connecting said grid of said third tube with the anode of saidfirst tube, means interconnecting said cathodes, an anode voltage supplysource having a positive terminal connected to said anodes, and acathode resistor connected to said cathodes and to the negative terminalof said source.

6. A scaleof-three multivibrator as claimed in claim 5 in whichcapacitors having the same.

values are shunted across said first, fourth and sixth resistors, andcapacitors having the same value lower than that of said firstmentionedca-r pacitors, are shunted across said second, third and fifthresistors. V a

7. A scale-of-three multivibrator as claimed in claim 5 in whichresistors shunted by capacitors are connected between said grids andsaid negative terminal of said source.

8. A scale-of-three multivibrator as claimed in claim 5 in whichcapacitors having the same value are shunted across said first, fourthand sixth resistors, and capacitors having the same value lower thanthat of "said first mentioned capacitors, are shunted across saidsecond, third and fifth resistors, and in which resistors shunted bycapacitors are connected between said grids and said negative terminalof said source.

9. A scale-of-three multivibrator comprising first, second and thirdelectron tubes each having a control grid, a cathode and an anode, afirst.

resistor connecting the grid of said first tube'with ,the anode of saidsecond tube, a second resistor connecting said grid of said first tubewith the anode of said third tube, a third resistor connecting the gridof said second tube with the anode of said first tube, a fourth resistorconnecting the grid of said second tube with the anode of said thirdtube, a fifth resistor connecting the grid means interconnecting saidcathodes, an anode voltage supply source having a positive terminalconnected to said anodes, a cathode resistor connected to said cathodesand to the negative terminal of said source, and grid resistorsconnected to said grids and said negative terminal of said source.

10. A scale-oi-three multivibrator as claimed in claim 9 in whichcapacitors are shunted across said second, third and fifth resistors,and capacitors having higher values than said first mentioned capacitorsare shunted across said first, fourth and sixth resistors.

11. A scale-of-three multivibrator comprising three electron tubes, eachhaving a cathode, a control grid and an anode, first and second voltagedividers connected in the anode-cathode circuit of each of said tubes,and means connecting the grid of each said tube to the first voltagedivider of one of said other tubes and to the second voltage divider ofthe other of said other tubes. I

12. A scale-of-three multivibrator comprising three electron tubes, eachhaving a cathode, a control grid, and an anode, a first and a secondvoltage divider connected in the anode-cathode circuit of each saidtube, said first voltage dividers having substantially identicaldividing characteristics and said second voltage dividers havingsubstantially identical dividing characteristics but different from thedividing characteristics of said first voltage dividers, and means 6connecting the first voltage divider of one 0! said tubes and the secondvoltage divider of another of said tubes to the control grid of theremaining one of said tubes.

13. A scale-of-three multivibrator comprising first, second, and thirdelectron tubes, each having a cathode, a control grid, and an anode, afirst and a second voltage divider connected in the anode-cathodecircuit of each said tube, said first voltage dividers havingsubstantially identical dividing characteristics and said second voltagedividers having substantially identical dividing characteristics butdifferent from the dividing characteristics of said first voltagedividers, means connecting the first voltage divider of said first tubeand the second voltage divider of said second tube to the grid of saidthird tube, means connecting the first voltage divider of the secondtube and the second voltage divider of the third tube to the grid ofsaid first tube, and means connecting the first voltage divider of saidthird tube and the second voltage divider of the first tube to the gridof said second tube.

JOHN W. TAYLOR, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

Article: Scale of N Counting Circuits, by Bradford Howland, from July1947 Electronicspages 138, 174, 176 and 178.

